1. Technical Field
A photolithography technique is disclosed, and more particularly to a photo mask, which reduces the difference in critical dimensions between patterns formed thereon, and a method for manufacturing patterns using the same is also disclosed.
2. Discussion of the Related Art
Photolithography techniques are known, in which patterns having designated shapes are formed on a wafer substrate using light. Such photolithography techniques have led to the high integration of a semiconductor device. Specifically, light, such as ultraviolet rays, an electron beam, or X-rays, is irradiated from an exposure apparatus to a position, at which patterns for insulating films or conductive films are formed, thus producing a photoresist, the solubility of which is changeable. A designated portion of the photoresist is exposed to light using a photo mask, and a part of the photoresist having a high solubility in a developing solution is removed. Thereby, photoresist patterns having designated shapes are obtained. By removing the part of the wafer, which is exposed from the photoresist patterns to the outside, by an etching step, semiconductor element patterns having desired shapes are formed.
FIG. 1 is a schematic view illustrating a conventional exposure apparatus. The conventional exposure apparatus comprises a condenser lens 20 for condensing light, such as a laser beam of an exposure source 10, a projection lens 40 for condensing the light into a wafer 50 arranged below the condenser lens 20, and a photo mask 30, having patterns 32 in designated shapes formed thereon, arranged between the condenser lens 20 and the projection lens 40 for patterning a photoresist 52 of the wafer 50.
In the above exposure apparatus, the laser beam irradiated from the exposure source 10 passes through the photo mask 30 through the condenser lens 20, is condensed by the projection lens 40, and is then transmitted to the wafer 50. Thereby, the patterns 32 on the photo mask 30 are projected on the photoresist 52 on the wafer 50.
In the case that a pattern, which is formed on a photo mask for a DRAM or a flash memory, is repeated and has a fine shape, the patterns on the photo mask are not projected onto the wafer in the same patterns, but are deformed so that the wafer patterns have critical dimensions (CDs) or a fidelity differing from desirable CDs or fidelity due to lens aberration of the exposure apparatus.
For example, in the case that each pattern formed on a wafer is a circular ring gate as shown in FIG. 2, an array of rectangular ring gate patterns 32 having vertically symmetrical structures are arranged on the photo mask.
Critical dimensions between the opposite ring gate patterns 32 having the vertically symmetrical structures are changed due to the lens aberration.
Photolithography techniques for embodying a high resolution to form finer patterns so as to meet high-integration and high-density trends of recent semiconductor devices are achieved by several methods, i.e., correction of a light source (for example, off-axis illumination), manufacture of a mask using optical interference effect (for example, attenuating phase shift, alternating phase shift, or etc.), and correction of the layout of a photo mask for preventing any optical proximity effect.
Accordingly, a photolithography technique for more precisely manufacturing fine patterns using the above methods must be studied and developed.